The invention relates to the general field of micro-fluidics with particular reference to system integration on a single chip.
Integrated micro-fluidic systems have many promising applications in medical treatment, industrial process control, biomedical analysis, etc. MEMS (micro electro-mechanical systems) is one of the most promising ways to implement various kinds of such integrated systems, because of the mass production potential offered by silicon wafers. However, most of the integrated devices developed so far, including micro fluidic handling and detection mechanisms, have utilized a multiple-wafer process. This has increased the difficulty of electronic integration and the cost of fabrication, and has degraded performance due to large fluidic or thermal parasitics. There is therefore a need for a single silicon wafer process to solve these problems.
There are several disclosed ways of fabricating micro fluidic devices using single silicon wafers [see references 1-4 below]. However, these techniques have many difficulties in integration of the micro fluidic control, thermal reactors or sensing/detection mechanism on-chip, due to the non-compatible process problem. Normally, large chambers (cavities) have been formed by wet etching/undercutting which provides poor process control. Moreover, integration of the active components (e.g., detectors/sensors, reactors, etc.) has not been implemented for the same reasons. In summary, a process for integrated fluidic systems e.g., micro-total-analysis-system (xcexcTAS) or lab-on-a-chip (LoC) using a single silicon wafer approach has thus far not been reported. The present invention seeks to disclose such a process.
1. Meint Boer et al, xe2x80x98Micromachining of buried micro channels in siliconxe2x80x99, J. Microelectromech. Systems, Vol.9, No.1, pp.94-103, 2000.
2. Quanbo Zou et al, CoMSaT: xe2x80x98A novel single-chip fabrication technique for three-dimensional MEMS, Sensors and Actuatorsxe2x80x99 A. 72, No. 2, pp. 115-124, 1999.
3. Quanbo Zou et al, xe2x80x98Single-chip fabrication of integrated fluid system (IFS)xe2x80x99, Proc. 11h IEEE MEMS98 Workshop, Heidelberg (Germany), pp. 448-453, January 1998.
4. J. Chen et al, xe2x80x98A high-resolution silicon monolithic nozzle array for ink jet printingxe2x80x99, The 8th International Conference on Solid-State Sensors and Actuators (Transducers ""95, and Eurosensors IX), Stockholm, Sweden, pp. 321-324, June 1995.
A routine search of the patented prior art was also performed with the following references of interest being found:
In U.S. Pat. No. 6,093,330 B1, Chong, et al. disclose a microfabrication process for enclosed microstructures using an anisotropic etch and an isotropic etch. Liu, et al., in U.S. Pat. No. 6,225,140, show a CMOS compatible surface machined pressure sensor. The pressure sensor is formed by etching a number of trenches in a substrate. Dielectric spacers are formed on the sidewalls of the trenches. The bottoms of the trenches are then etched using isotropic etching to undercut the trench sidewalls. U.S. Pat. No. 6,075,269 (Terasawa, et al.) discloses a device that includes a recessed portion formed by isotropic-etching, then anisotropic etching and isotropic etching while Shaw et al. in U.S. Pat. No. 5,719,073 show microstructures and use a single mask, single-crystal process for fabrication thereof.
It has been an object of at least one embodiment of the present invention to provide a process for manufacturing a complete micro-fluidic system contained on a single chip.
Another object of at least one embodiment of the present invention has been that said process utilize only dry etching.
Still another object of at least one embodiment of the present invention has been that said process include sub-processes to manufacture micro-chambers having a high degree of thermal isolation as well as low thermal mass.
A further object of at least one embodiment of the present invention has been that said process include sub-processes to manufacture micro-pumps.
These objects have been achieved by an improvement over the state of the art fabrication processes for integrated micro-fluidic systems, including liquid handling, reaction and on-chip sensing/detection which are normally multi-wafer fabrication procedures. These complicated prior art processes increase the fabrication cost and degrade the performance of the system. A few single silicon wafer approaches in the literatures have stated difficulty in the micro-fluidic control and on-chip sensing/detection. The thermal reactors disclosed so far have used multi-wafer process, which has limited the integration and the disposability of the devices. The present invention uses only dry etch processes to form micro-chambers. In particular, it makes use of deep reactive ion etching whereby multiple trenches of differing depths may be formed simultaneously. Buried micro-chambers are formed by isotropically increasing trench widths using an etchant that does not attack the mask so the trenches grow wider beneath the surface until they merge. Deposition of a dielectric layer over the trenches allows some trenches to be sealed and some to be left open. Micro-pumps are formed by including a layer in the micro-chamber roof. This layer is used to change chamber volume either through electrostatically induced motion or through thermal mismatch as a result of its being heated.